The present invention relates to a formulation for treating, controlling and preventing parasitic worm infestations and a method for making the formulation. More specifically, the present invention relates to a combination roundworm and tapeworm parasiticide for use in horses and household pets.
Several types of parasites, including cestodes, nematodes and obligate parasitic insects, particularly flies, commonly plague horses, dogs and cats. Cestodes are flatworms and include, for example, tapeworms, while nematodes are roundworms. Avermectins and milbemycins are nematocidal agents commonly used in the treatment and control of parasitic roundworm infestations in equines, including domestic horses, donkeys, mules and zebras, as well as in companion animals, namely cats and dogs. These agents are also effective against obligate parasitic flies. Contrary to popular belief among animal owners, however, these agents are ineffective against tapeworm infestations. Rather, tapeworm infestations must be controlled and treated by a cestocidal agent.
Studies have shown that misinformation about tapeworm treatment and control is common among horse owners. Many horse owners evidently believe that ivermectin, an avermectin used for treating and controlling roundworm infestations, is effective in controlling tapeworm infestations as well. This misinformation may account for a rise in the prevalence of certain tapeworms. A particular equine tapeworm whose prevalence is on the rise is Anoplocephala perfoliata. 
Tapeworms are pervasive parasites that appear to infect at least half of all mature horses. Post-mortem studies have shown that, in general, at least 50% of mature horses in many populations are infected with A. perfoliata. A. perfoliata is a type of tapeworm that can infect all types of equine animals. Adult A. perfoliata attach to the posterior regions of the equine intestinal tract. The highest concentration is in the cecal wall but a fair amount attach to the terminal ilium and ventral colon as well. The greatest concentration of A. perfoliata, and thus the greatest associated damage, occurs at the ileocecal junction. A. perfoliata infestation increases the incidence of spasmodic colon and ileal impaction in horses. Tapeworms also have been implicated as a cause of cecal and ileocecal intussusceptions in young horses. The latter conditions are potentially fatal and can be remedied only by complicated and expensive abdominal surgery.
There are only a few classes of drugs which are effective in the treatment, control and prevention of tapeworm infestations. Among these classes are praziquantel, pyrantel and morantel compounds. Parasiticidal formulations have been disclosed which contain praziquantel combined with a variety of roundworm controlling agents. One such formulation is disclosed in U.S. Pat. No. 5,824,653 to Beuvry et al. The compounds which result from these combinations, however, may be dangerous as praziquantel has been shown to be toxic at levels other than low dosages. Additionally, praziquantel purportedly is bitter to taste making it unpalatable and thus undesirable in ingestable formulations, for example, pastes.
Pyrantel and morantel compounds are currently believed by those skilled in the art to offer an inadequate substitute to praziquantel in the treatment and control of tapeworm infestations. Pyrantel salts generally either are only partially effective against tapeworms at their label dosages (e.g., pyrantel pamoate) or must be administered in daily regimes (e.g., pyrantel tartrate). Further, pyrantel pamoate offers a low suspended solids content when in paste form, the highest percentage encountered being about 43.95% weight per weight (w/w). A paste with a low suspended solids content contains less active ingredient per unit than a paste with a higher suspended solids content. Therefore, a higher volume of paste must be delivered to the animal in order to achieve the same therapeutic effect.
Accordingly, there remains a need in the veterinary industry for a combination parasiticidal formulation containing both a cestocidal agent and an agent effective against nematodes and obligate parasitic flies that is less toxic than formulations containing praziquantel. Further, a palatable combination parasiticide is needed for administration in ingestable forms. The primary objective of this invention is to meet these needs.